It's called From the Corner of His Eye. He's not time traveling, he just figured out how to hop between different alternate realities. It happens to be one of my favourite books.

[–] Restaldt@lemmy.world 3 points 10 months ago (1 children)

Ive been trying to figure this out all day and thats not it

Im pretty sure ive conflated parts of Mr murder and a completely different author/book called the mark of the assassin and honestly maybe parts of a 3rd book i havent remembered yet

I read those ~15 years ago

[–] dona1dquixote@lemm.ee 3 points 10 months ago

Well then that's a weird coincidence because From the Corner of His Eye is about a child genius who can move between different realities and is being targeted by a serial killer.